1. Field of the Invention
The present invention relates to wireless communication; and, in particular, relates to wireless communication using radiation in the infrared (IR) range of frequencies ("IR frequencies").
2. Discussion of the Related Art
Wireless communication using IR frequencies have been used extensively in remote control applications of appliances and consumer electronics products. Recently, IR transceivers are also used for data communication applications in devices such as personal digital assistants (PDAs) and portable computers.
In the past, for remote control applications in appliances and consumer electronic devices, a 38 KHz amplitude shift-key (ASK) informal standard (the "VCR" standard) is widely used among manufacturers to allow interoperability of IR remote control devices. Today, however, most PDAs and portable computers use different signal modulation schemes and proprietary communication protocols. For example, the "Wizard" line of "palmtop" computers, from Sharp Electronics Corp., and the "Newton" PDAs, from Apple Computers Inc. share a common protocol and a 500 KHz ASK signal modulation scheme ("SHARP" modulation scheme and protocol), which is not compatible with IR transceivers in other palmtop computers, such as those manufactured by Hewlett-Packard company, which use a signal modulation scheme ("HP-SIR scheme") involving a single signal pulse per period.
For IR communication to achieve wide acceptance in data communication applications, a uniform signal modulation scheme and communication protocol ("uniform IR communication standard") is required, for example, in an IR-linked network. Such a uniform IR communication standard allows communication among a potentially large number of devices, such as portable computers, printers, file servers, and other desktop computers and workstations. For this purpose, the "Infrared Data Association" (IrDA) is formed to propose such a uniform IR communication standard ("IrDA standard") for all IR data communications. At this time, the IrDA standard uses the HP-SIR scheme at the "physical layer" and an HLDC-SIR communication protocol at the "link layer". This IrDA standard supports these bit rates: 2.4 Kbps, 9.6 Kbps, 19.2 Kbps, 38.4 Kbps, 57.6 Kbps, and 115.2 Kbps.
Because of the large number of communication standards used in today's IR communication, at both the physical and the link layers, a communication device which handles all the underlying signal modulation and protocol translations to allow two or more IR-capable devices to communicate without user intervention is clearly desirable. Furthermore, an external communication device which can be used as an attachment to provide an electronic device IR capability is also desired.
Unlike remote control applications, in which only one-way communication is required, most data communication applications are bidirectional: i.e. data is both received and transmitted in each device. In IR communication, unlike most other media, proper reception in a device's receiver can be interfered by reflections ("echoes") of the device's own transmitted signal. Two undesirable side effects can result from such an interference. First, the reflected signal can be mistaken for a signal to be received. Second, the strength of a device's own echo can interfere with the receiver's automatic gain control (AGC) circuit, which is often present in a receiver circuit to automatically compensate for signal strength of the incoming signal. Such an interference results in a high error rate because of improper amplification of the received signal. To alleviate these undesirable effects, two solutions are proposed: (i) echoes can be eliminated by software and (ii) AGC circuits should not be used. However, neither solution is satisfactory because (i) elimination of echoes by software is a complex operation, leading to undue complexity in the resulting circuit, and (ii) AGC circuits are desirable because the device must adapt to a wide range of signal strengths and environmental conditions under which a device using IR communication can be used.